Creating Biomorphic Barbed and Branched Mesostructures in Solution through Block Copolymer Crystallization

Synergetic Self-Assembly of Liquid Crystalline Block Copolymer with Amphiphiles for Fabrication of Hierarchical Assemblies

Novel functions and advanced structure, where each single component could not be produced individually, can exhibit from the collective and synergistic behavior of component systems. This synergetic strategy has been successfully demonstrated for co-assembly of polymer-polymer to construct hierarchical nanomaterials. However, differences in the natures of polymer and small molecules impose challenges in the construction of sophisticated co-assemblies with geometrical and compositional control. Herein, a synergetic self-assembly strategy is proposed to prepare organic-organic hybrid colloidal mesostructures by blending a liquid crystalline block copolymer (LC-BCP) with small molecular amphiphiles. Through a classic solvent-exchange process, amphiphiles embedded with LC-BCP realize multi-component nucleation and hierarchical assembly driven by anisotropic interaction from the LC ordering alignment of the core-forming block. 1D nanofibers with a periodic striped structure are formed by further LC component fusion and refinement. In addition, LC ordering effect of LC-BCP can be regulated by selecting appropriate solvents and leads to the formation of vesicular co-micelles. By means of the thermal-responsive behavior of amphiphiles, hexagonal pore arrays are finally generated on the surface of those vesicles.

Polyferrocenylsilane Block Copolymer Spherulites in Dilute Solution

Self-assembly of block copolymers (BCP) into uniform 3D structures in solution is an extremely rare phenomenon. Furthermore, the investigation of general prerequisites for fabricating a specific uniform 3D structure remains unknown and challenging. Here, through a simple one-pot direct self-assembly (heating and cooling) protocol, we show that uniform spherulite-like structures and their precursors can be prepared with various poly(ferrocenyldimethylsilane) (PFS) BCPs in a variety of polar and non-polar solvents. These structures all evolve from elongated lamellae into hedrites, sheaf-like micelles, and finally spherulites as the annealing temperature and supersaturation degree are increased. The key feature leading to this growth trajectory is the formation of secondary crystals by self-nucleation on the surface of early-elongated lamellae. We identified general prerequisites for fabricating PFS BCP spherulites in solution. These include corona/PFS core block ratios in the range of 1-5.5 that favor the formation of 2D structures as well as the development of secondary crystals on the basal faces of platelets at early stages of the self-assembly. The one-pot direct self-assembly provides a general protocol to form uniform spherulites and their precursors consisting of PFS BCPs that match these prerequisites. In addition, we show that manipulation of various steps in the direct self-assembly protocol can regulate the size and shape of the structures formed. These general concepts show promise for the fabrication and optimization of spherulites and their precursors from semicrystalline BCPs with interesting optical, electronic, or biomedical properties using the one-pot direct self-assembly protocol.

Hierarchical Approach for Controlled Assembly of Branched Nanostructures from One Polymer Compound by Engineering Crystalline Domains

The interplay of crystalline packing, which governs atomic length-scale order, and hierarchical assembly, which governs longer length scales, is essential to fabricate complex superstructures from polymers for many applications. Here, we demonstrate that a diblock copolymer containing an N-octylglycine peptoid block, which has a propensity to crystallize, can form distinct hierarchical superstructures including a star-like morphology, a superbrush, or a nanosheet by tuning the balance between surface energy arising from the solubility of the copolymers and crystallization energy of the solvophobic polypeptoid blocks. We show that partially ordered micellar aggregates (clusters) are key intermediates that form early in the assembly process and template the formation of superstructures via the oriented fusion of individual micelles as the growth materials. Notably, the fiber-like branch of the superstructures is driven by crystallization and exhibits growth in a living linear manner. The superstructures can be internalized by mammalian cells and hold promise for biomedical applications.

Spherulite-Like Micelles

One-dimensional (1D) and 2D structures by crystallization-driven self-assembly of block copolymers (BCPs) can form fascinating hierarchical structures through secondary self-assembly. But examples of 3D structures formed via hierarchical self-assembly are rare. Here we report seeded growth experiments in decane of a poly(ferrocenyldimethylsilane) BCP with an amphiphilic corona forming block in which lenticular platelets grow into classic spherulite-like uniform colloidally stable structures. These 3D objects are spherically symmetric on the exterior, but asymmetric near the core, where there is a more open structure consisting of sheaf-like leaves. The most remarkable aspect of these experiments is that growth stops at different stages of growth process, depending upon how much unimer is added in the seeded growth step. The system provides a model for studying spherulitic growth where real-time observations on their growth at different stages remains challenging.

Formation of 2D and 3D multi-tori mesostructures via crystallization-driven self-assembly

The fabrication of three-dimensional (3D) objects by polymer self-assembly in solution is extremely challenging. Here, multi-tori mesostructures were obtained from the crystallization-driven self-assembly of a coil-crystalline block copolymer (BCP) in mixed solvents. The formation of these structures follows a multistep process. First, the BCP self-assembles into amorphous micrometer-large vesicles. Then, the BCP confined in these mesosized vesicles crystallizes. This second step leads to the formation of objects with shapes ranging from closed 3D multi-tori spherical shells to 2D toroid mesh monolayers, depending on the solvent mixture composition. This approach demonstrates how topological constraints induced by the specific interactions between coil-crystalline BCP and solvents can be used to prepare mesostructures of complex morphologies.

Inky flower-like supermicelles assembled from π-conjugated block copolymers

Conjugated block copolymers PPV₇-b-P2VP_n are utilized as building blocks to construct inky flower-like hierarchical supermicelles. The assembly process is tracked and the control of morphology is successfully realized.

Moebius strips of chiral block copolymers

The Moebius topology (twisted, single-sided strip) is intriguing because of its structural elegance and distinct properties. Here we report the generation of block copolymer Moebius strips via a fast self-assembly of chiral block copolymer polystyrene-block-poly(D-lactide acid) (PS-b-PDLA) in tetrahydrofuran/water mixed solvents. The Moebius strip is formed by morphological evolution from large compound micelle (LCM) to spindle-like micelle (SLM) and then to toroid with a 180° twist along the ring. Mechanism insight reveals that a subtle balance of crystallization of PDLA and microphase separation between PS and PDLA chains dominates the formation of Moebius strips. An intriguing helix-helix transition occurs during the chiral transfer from microphase to assemblies, which is driven by relaxation of the internal stress within SLM related to orientated stretching of PS chains. Mesoporous chiral channels can be generated within Moebius strips after removal of PDLA, which are interesting in chiral recognition, separation and asymmetric catalysis.